Assessing the role of plasma-engineered acceptor-like intra- and inter-grain boundaries of heterogeneous WS(2)–WO(3) nanosheets for photocurrent characteristics

High-temperature annealing in tungsten disulfide resulted in heterogeneous WS(2)–WO(3) in which intra- (within WS(2) and WO(3)) and inter- (between WS(2) and WO(3)) grain boundaries were observed, which were highly critical for charge transport and recombination. The heterogeneous WS(2)–WO(3) phase was evidenced by observing the coexistence of d-spacing values of 0.26 nm (WS(2)) and 0.37 nm (WO(3)) in transmission electron microscopic (TEM) studies. Further systematic high-resolution TEM studies elucidated that intra-grain boundaries separated crystallites within WS(2) and WO(3), while inter-grain boundaries separated WS(2) from WO(3). As WS(2) and WO(3) are both n-type, these defects are acceptor-like in the grain boundaries and they actively participate in the capture (trapping) process, which impedes charge transport characteristics in the heterogeneous WS(2)–WO(3) films. Plasma treatment in the heterogeneous WS(2)–WO(3) film, for 60 minutes using argon, energetically modulated the defects in the intra/inter-grain boundaries, as evidenced from detailed comparative photocurrent characteristics obtained individually in (i) pristine WS(2), (ii) heterogeneous WS(2)–WO(3) and (iii) Ar plasma-treated heterogeneous WS(2)–WO(3) films under blue and green lasers, along with AM1.5 (1 sun) illumination. Detrimental roles (trapping/de-trapping and scattering) of grain boundary states on photoelectrons were seen to be significantly suppressed under the influence of plasma.